Catalase enzyme (EC 22.214.171.124) was immobilized by entrapping in cellulose acetate beads. This organic matrix is highly resistant to mechanical stability and can be used under various conditions. Initial studies were conducted to examine the immobilization ability of catalase on the matrix previously activated with a series of reagent normally and the best results were obtained with the beads activated with Ce(SO4)(2), In the optimization studies of the immobilized enzyme optimum pH and temperature were found as pH:7.0 (Tris-HCl, 50 mM) and 35degreesC. In the characterization studies of the immobilized enzyme some parameters such as storage and thermal stability were investigated. Finally, the immobilized enzyme was used for the decomposition of hydrogen peroxide in milk samples and also by using a catalase biosensor prepared the decomposition level of hydrogen peroxide was detected.